Manufacture of hydrocyanic acid



Patented June 9, 1936 UNITED STATES PATENT OFFICE MANUFACTURE OF HYDROCYANIC ACID Russell W. Millar, Berkeley, Calif., assignor to Shell Development Compan San Calif., a corporation of Delaware No Drawing. Application June Francisco,

Serial No. 677,463 15 Claims. (01. 23-151)- This invention relates tothe production 01 bydrocyanic acid from mixtures of saturated allphatic hydrocarbons, oxides of nitrogen and hiing the thermal treatment of the parafiine hydrocarbons or their mixtures in the presence of an oxide of nitrogen, the nitrogen being present in relatively substantial amounts.

The process is preferably carried out in the absence of hydrogen and/or substantial amounts of water vapor since both substances unfavorably influence the reaction, thereby decreasing the possible yield of hydrocyanic acid. It is therefore desirable to avoid the extraneous introduction of these substances into the reacting mixture.

The output of hydrocyanic acid increases with an increase in the percentage of nitrogen in a mixture of nitrogen, oxides of nitrogen and saturated aliphatic hydrocarbon. A desirable ratio is one wherein NzNO is greater than about 3.5:1, preferably about 4:1 to 8:1 or higher. On the other hand, excellent results are obtained using a mixture wherein the ratio of hydrocarbon to nitric oxide is substantially 3.5: 1 or greater. Operating with methane or natural gas, the following approximate proportions have been found excellent: CH4 or natural gas) 4: nitric oxide 1: nitrogen 8. y

In lieu of natural gas, there may be utilized industrial gases containing. paraihne hydrocarbons, such as coal gas, coke oven gas, gas from oil cracking plants, gas from destructive hydrogenation plants and the like. Free hydrogen may be removed from any of these mixtures prior to the thermolytic treatment, the removal or extraction step being carried out by any conventional method such as diffusion, absorption, etc.

The process can be carried out in the absence or presence of .a catalytic agent amongst which may be described, active'carbon, carborundum, sillimanite, A1203, silica, charcoal, quartz. If carried out in a heated tube, the reaction chamber therein 'may be unobstructed or may be packed with or may contain one or more of the catalytic substances. For the sake of steady operation, packing is preferably employed.

The yield of hydrocyanic acid increases rapidly with a rise in temperature of operation and after a practical optimum temperature increases but I slowly. For example, working with a mixture containing natural gas or methane at about atmospheric pressure, the yield of hydrocyanic acid rapidly increases up to 1200 C. and then slowly increases up to about 1400 C. where the declining rate of increase no longer becomes of practical interest due to heat consumption and other uneconomical factors. With ethane, propane; isobutane, butane and the higher homologues of methane and their mixtures, higher yields are obtained at temperatures lower than 1200" C. than with natural gas.

Working with similar mixtures of CH4, NO, and. N2 under identical conditions, other than temperatures, the following conversions of NO to HCN were noted:

I Degree 0. 45% conversion at 1100 83% conversion at 1200 84.6% conversion at 1400 The time of residence of the reaction mixture in the reaction space has a great influence on the yield of hydrocyanic acid, which, for a given mixture of reactants, temperature, and catalyst, passes through a maximum as the time of residence in the reaction space is increased. I have found a period of from 1 to 2 seconds entirely satisfactory, although it is understood that at relatively high temperatures, shorter periods may be resorted to while at lower temperatures or at higher temperatures with large amounts of inert diluents, longer periods may be resorted to. Shorter periods may also be experienced with certain of the catalysts as will be apparent hereinafter.

An excess of the hydrocarbon increases the yield of hydrocyanic acid, but the advantage above 4-5 fold is small. The presence offree oxygen, in at least small amounts, does not appear to decrease the yield of hydrocyanic acid appreciably.

In lieu of nitric oxide, there may be employed nitrogen peroxide, nitrous anhydride, nitrogen tetroxide, nitrogen pentoxideand nitrous oxide. All these compounds yield nitric oxide upon heating, which is very stable and yet readily active.

2 2,040,000 tive purposes only. and to disclose ttie innu'tence M W or effect of the variable factors as mpera ure, Temperature 1200, c

rate of cool excess hydro- 031503? 1 ;32 1 etc. mg Time of 1.7-2.0 seconds 5 Exam 1 q lilfl m 5 Catalyst: silica I r1010 N0. mm Natural Time 0! 111010 011 7 p251: 10

3? Pisa. v10

Diamotl' ofthareaction Tuba 0.5 111.: 1200 2 1 2 1.50 500 2:11.... 00.0 1200 4 1 4 1.02 1 0 11.0 2:: s: as 13 i4 3: 410 0.50 04.0 L 15 0015 Exam-III 02.0

Natural gas: N0:N2=4:1:4 Temperature. 1200' The mixture of nitrogen and nitric oxide can 20 catalyst: sili a be obtained by the'oxidation of ammonia, the

hydrocarbon or hydrocarbons beingadded tothe oxidation mixture, from which water, preferably,

93 lfig has been removed. Sufllcient natural gas or parafline hydrocarbon should be added to make the ratio of CnH2n+2 to nitric oxide, at least about 61.3 15% 00.4 3.5 or 4 to 1. The ratio of NO to N m the oxidak: 7 1:; tion mixture should be about'l:7.5 to 1:8. 5.2 50.6

rious catalysts on the time of heating:

Sillimanite and cafliorundum.

Temperature 1200 C. I Gas: NO :1v2=4-1-s Diameter of tube, 1.0 in.

detail the preferred embodiment of my invention and some variants thereof, it will be understood As shown by Example 111, the yield is increased that this is only for the purpose of making the by rapid cooling of the reaction products after invention more clear and that the invention is 75 they have left the reaction space. not to be regarded as limited to the details of 75 The following table shows the influence of va- 30 8illimanite Carbonmdum Silica No 00mm 40 40 Time of Yield on Time of Yield on Time of Yield on Time of Yield on heatinmsoc. N0, percent heating, sec. N0, heating, sec. N0, percent heating, sec. N0, percent Exam III It will be noted that catalysis materially reduces the time of contact. e T mpemture 1200 c The concentration of hydrocyanicacid in the Natural exit gas varies up to above 6% and the HON may Time of heating 1.66 to 1.67 sec. be recovered by any of the conventional modes. 60

can 8mm It may be recovered as an alkali cyanide and v regenerated by means of a mineral acid or may be recovered per se by means of a scrubbing v agent or solvent which'is'subsequently subjected Yi d N Reaction tube Exit tube to distillation or the like I s 65 Mt diam? It is extremely desirable that iron or ferrous alloys be absent or out of contact with the mamam m terials undergoing reaction as iron is catalytically g 15I0 2 0mm. favorable to the deposition of carbon. 7o 8M While I have in the foregoing described in some 2,048,980 operation described, nor is it dependent upon I the soundness or accuracy of the theories which I have advanced as to the reasons for the advantageous results attained. On the other hand, the invention is to be regarded as limited only by the terms of the accompanying claims, in which it is my intention to claim all novelty inherent therein as broadly as is possible in view of the prior art.

I claim as my invention:

1. A process of producing hydrocyanic acid which comprises heating a saturated aliphatic hydrocarbon to a temperature not less than about 1200 C. in the presence of a substantial amount of nitrogen and an oxide of nitrogen in the substantial absence of water.

2. A process of producing hydrocyanic acid which comprises heating a saturated aliphatic hydrocarbon to an elevated temperature in the presence of a substantial amount of nitrogen and nitric oxide for a period not substantially greater than two seconds in the substantial absence of water.

3. A process of producing hydrocyanic acid which comprises heating a saturated aliphatic hydrocarbon to an elevated temperature in the presence of nitrogen and preformed nitric oxide wherein the ratio of hydrocarbon to nitric oxide is greater than 3.5:1 in the substantial absence of water.

4. A process of producing hydrocyanic acid which comprises heating a saturated aliphatic elevated temperature in the presence of nitrogen and preformed nitric oxide, in the proportion not less than 3.5: 1, respectively in the substantial absence of water.

5. A process of producing hydrocyanic acid which comprises heating a saturated aliphatic hydrocarbon to an elevated temperature in the presence of nitrogen and preformed nitric oxide, the ratio of hydrocarbon to nitric oxide being at least 3.5:1 and the ratio of nitrogen to nitric oxide being at least 35:1 in the substantial absence of water.

6. A process of producing hydrocyanic acid which comprises heating methane to at least 1200 C. in the presence of nitrogen and preformed nitric oxide in the substantial absence of water.

7. A process of which comprises producing hydrocyanic acid heating methane to at least 1200 C. in the presence of nitrogen and preformed nitric oxide, the methane being in excess of that amount capable of conversion under the conditions of operation in the substantial absence of water.

8. A process of producing hydrocyanic acid which comprises heating methane to at least about 1200 C. in the presence of nitrogen and preformed nitric oxide, the proportions of CH4: NO:N being at least 4:124 in the substantial absence of water. I

9. A process of producing hydrocyanic acid which comprises heating natural gas to at least about 1200 C. in the presence of nitrogen and preformed nitric oxide, the proportions of natural gas: NO:N being about 4:1:8 in the substantial absence of water.

10. A process of producing hydrocyanic acid which comprises heating a saturated aliphatic hydrocarbon to at least about 1200 C. in the presence of nitrogen, preformed nitricoxide and a hydrocyanic acid forming catalyst in the substantial absence of water.

11. A process of producing hydrocyanic acid which comprises heating a'saturated aliphatic hydrocarbon to at least about 1200 C. inthe presence of nitrogen, preformed nitric oxide and sillimanite in the substantial absence of water.

12. A process of producing hydrocyanic acid which comprises heating a saturated aliphatic hydrocarbon to at least about 1200 C. in the presence of nitrogen, preformed nitric oxide and carborundum in the substantial absence of water.

13. A process which comprises heating a saturated aliphatic hydrocarbon to at least about 1200 C. in the presence of nitrogen, preformed nitric oxide and silicia in the substantial absence of water.

14. A process of producing hydrocyanic acid which comprises oxidizing ammonia with an amount of oxygen-containing gas so as to obtain a mixture of nitrogen and an oxide of nitrogen, substantially removing the water content thereof, subsequently adding thereto a saturated aliphatic hydrocarbon and heating the mixture to an elevated temperature version of hydrocarbon to hydrocyanic acid is attained.

15. A process of producing hydrocyanic acid which comprises oxidizing ammonia with an amount of oxygen-containing gas so as to obtain a mixture of nitrogen and an oxide of nitrogen,

' substantially removing the water content thereof, subsequently adding thereto natural gas and heating the mixture to an elevated temperature until substantial conversion of hydrocarbon to hydrocyanic acid is attained.

RUSSELL W. MILLAR.

until substantial conof producing hydrocyanic acid 

